In a large bowl sift together the flour, sugar and salt. Cut in the cold butter and mix with your fingers until you have a fine bread crumb texture. Start pouring in the water a little at a time, mixing with your hands as you go. It will start to come together quite quickly. Once the dough stays to together you won't need to add any more water. Gently knead the pastry and fold it over on to itself a few times. Divide into two balls, wrap and refrigerate for about an hour.
Peel, core and dice the apples into about 1-inch pieces.
In a medium skillet set over medium heat, melt the butter and brown sugar. When it starts to bubble add the apples. Stir well to coat them completely. Reduce heat to low, cover and stir occasionally until they are fully cooked. This will take about 20 minutes. The apples will be soft and golden when done. When they are just about cooked, add the cinnamon, nutmeg, vanilla and give a good stir. Remove from heat and set aside.
Preheat oven to 375 degrees F and remove your dough from the fridge. On a floured surface roll out each dough ball until it about 1/4 inch thick. Using a 3 inch circle cutter, cut out all of your circles for the pastry bottoms.
Cut the second pastry sheet into 1/2 inch strips. Then cut the strips cross ways to about 4 inches in length. These strips will be used to make the lattice topping.
Gently press the pastry into each tin. Fill each pastry case with the filling and top with a lattice topping. To make the lattice topping, use four strips of pastry, like you see in the photos.
Whisk the egg in a small bowl. Brush the lattice topping with the egg wash and sprinkle over a little sugar. Bake between 15 - 20 minutes or until golden and the pastry is fully cooked and flaky. Allow to cool in muffin tins and remove once cooled.